1. Field of the Invention
The present invention relates to a method and an apparatus for slidingly contacting a superfinishing stone with a raceway surface formed in an outer ring of a tapered roller bearing to thereby superfinish the raceway surface and, more particular, to an improved technology which can avoid an interference between the superfinishing stone and the outer ring.
2. Description of the Related Art
Conventionally, to superfinish a raceway surface of an outer ring of the tapered roller bearing, for example, there is used such a superfinishing apparatus 1 as shown in FIG. 7. The superfinishing apparatus 1 includes a backing plate 5, a pair of pusher rollers 7 (only one of them is shown), a pair of shoes 9 (only the lower portion is shown), a superfinishing stone holder 13, a superfinishing stone clamp bolt 17, a pressurizing cylinder 21 and an oscillation table 23. The backing plate 5 causes an outer ring 3 to rotate. The pair of pusher rollers 7 pushes the outer ring 3 against the backing plate 5. The shoes 9 support the outer ring 3 on the lower and lateral sides thereof. The superfinishing stone holder 13 supports a superfinishing stone 11 at a leading end portion thereof. The clamp bolt 17 is threadedly engaged with the leading end portion of the superfinishing stone holder 13 for fixing the superfinishing stone 11 through a superfinishing stone holding plate 15. The pressurizing cylinder 21 moves the superfinishing stone holder 13 in a direction where the superfinishing stone 11 is pushed against a raceway surface 19. The oscillation table 23 moves the superfinishing stone holder 13 and the pressurizing cylinder 21 in such a manner that the superfinishing stone 11 can approach or move away from the backing plate 5.
And, when the backing plate 5 rotates, the outer ring 3, which is placed on the shoes 9 and is pushed by the pusher rollers 7, is rotated in synchronization with the backing plate 5. Next, the superfinishing stone 11 is moved toward the inner periphery of the outer ring 3 by the oscillation table 23 and the pressurizing cylinder 21 is driven, so that the leading end face of the superfinishing stone 11 is pressed against the raceway surface 19 of the outer ring 3. The superfinishing stone 11 is disposed perpendicular to the raceway surface 19 and the leading end face of the superfinishing stone 11 is slidingly contacted with the raceway surface 19.
The superfinishing stone 11, the leading end portion of which has been worn due to such superfinishing, is moved from the inner periphery of the outer ring 3 to the outside. After then, the superfinishing stone clamp bolt 17 is loosened, whereby the superfinishing stone 11 is fed out to the leading end side thereof. And, by tightening the superfinishing stone clamp bolt 17 again, the superfinishing stone 11 is manually fed out sequentially from the leading end side thereof and is consumed accordingly.
However, in the above-mentioned conventional superfinishing apparatus 1, as shown in FIG. 8, since the superfinishing stone 11 is disposed perpendicular to the raceway surface 19 of the outer ring 3, a non-working raceway surface 19b located on the opposite side to a working raceway surface 19a and a rear end portion 11a of the superfinishing stone 11 interferes with each other, which limits the length of the superfinishing stone 11 to be used. Therefore, when an outer ring having a small bore diameter is superfinished, it is necessary to use a short superfinishing stone that can be inserted into the inner periphery of the outer ring, which increases the frequency of replacement of the superfinishing stone, resulting in the lowered operation efficiency. Also, a superfinishing stone requires a clamp portion which is not used and, therefore, in the case of a short superfinishing stone, the clamp portion to be wasted increases, which results in the uneconomical superfinishing stone. Further, the interference of the superfinishing stone rear end portion with the non-working raceway surface of the outer ring not only, as described above, disables use of a long superfinishing stone but also provides an obstacle to realization of an automatic superfinishing stone feed-out mechanism which automatically feeds out the superfinishing stone depending on the consumption.
The present invention aims at eliminating the above drawbacks found in the conventional method and apparatus for superfinishing a tapered roller bearing. Accordingly, it is an object of the invention to provide a method and an apparatus for superfinishing a tapered roller bearing which can reduce the frequency of replacement of superfinishing stones to thereby enhance operability, can enhance the economy of consumption of a superfinishing stone, and can realize automated feed-out of the superfinishing stone.
In attaining the above object, according to a first aspect of the invention, there is provided a superfinishing method of a tapered roller bearing, including the steps of: rotating an outer ring of the tapered roller bearing about a center axis thereof; inserting a straight-shaped superfinishing stone from a front face of outer ring; and slidingly contacting a leading end face of the superfinishing stone with a taper-shaped raceway surface formed in an inner peripheral surface of the outer ring to thereby superfinish the raceway surface. The superfinishing stone is inclined outwardly of the front face of outer ring with respect to a vertical line of the raceway surface.
According to the superfinishing method of the first aspect, since the superfinishing stone is inclined outwardly of the front face of outer ring with respect to the vertical line of the raceway surface, there can be avoided interference between the rear end portion of the superfinishing stone and the non-working raceway surface located on the opposite side to the working raceway surface, thereby removing a length limit of the superfinishing stone. Accordingly, the superfinishing stone can increase the length thereof, which can reduce the frequency of replacement of superfinishing stone. And, the elimination of interference of the rear end portion of the superfinishing stone makes it possible to employ a superfinishing stone feed-out mechanism which sequentially feeds out the long-sized superfinishing stone depending on the consumption of the superfinishing stone. That is, the present superfinishing method can remove an obstacle to an automated superfinishing apparatus.
And, in the present superfinishing method, the inclination angle of the superfinishing stone with respect to the vertical line of the raceway surface may be preferably in the range of 5xc2x0-25xc2x0 in almost all bearings. When the taper half angle of the raceway surface is small, the inclination angle may be more preferably in the range of 10xc2x0-20xc2x0, and when the outer ring width is large, the inclination angle is further preferably in the range of 15xc2x0-20xc2x0.
That is, according to the superfinishing method of the tapered roller bearing, since the inclination angle of the superfinishing stone with respect to the vertical line of the raceway surface is in the range of 5xc2x0-25xc2x0, not only there can be prevented interference between the rear end portion of the superfinishing stone and the non-working raceway surface located on the opposite side to the working raceway surface, which can be caused when the inclination angle is less than 5xc2x0, but also there can be prevented from chipping the sharpened shape of the leading end portion of the superfinishing stone, which can be caused when the inclination angle is more than 25xc2x0.
In the superfinishing working, it is generally known that the surface pressure of superfinishing stone is an important element of the working conditions. Therefore, in case where the contact area S of superfinishing stone on the working surface increases, the pressurizing force of the superfinishing stone is increased so as to secure the surface pressure of the superfinishing stone. That is, in a state where the contact area S of a superfinishing stone increases, in most cases, since the length of the superfinishing stone in the peripheral direction of a work (outer ring) increases, such increased superfinishing stone pressurizing force has little influence on the shearing force that acts on the superfinishing stone per unit superfinishing stone length in the peripheral direction.
On the other hand, as in the present invention, in case where the superfinishing stone is inclined at an angle of xcex8, as shown in FIG. 1, since a surface pressure f is a component of the pressurizing force F of the superfinishing stone (a component acting perpendicularly onto the raceway surface of the outer ring; f=F cos xcex8/S), it is necessary to increase the pressurizing force F over the conventional method. And, as xcex8 increases, the pressurizing force F need to be increased exponentially in order to obtain a constant surface pressure f (for example, in the case of xcex8=25xc2x0, the pressurizing force F is increased about 10% when compared with xcex8=0xc2x0). Also, according to the invention, since the leading end portion of the superfinishing stone is sharpened to thereby reduce the area thereof that receives a shearing force. Thus, when xcex8 is increased, the leading end portion of the superfinishing stone can be chipped easily. Such chipping is easy to occur when, in the working start time, the superfinishing stone moves down and is contacted with a work more often than in the normal working time. The condition in this time varies according to the work rotation speed and the superfinishing stone oscillation speed in the roughing time and in the finishing working time, the specifications of bearings, and the kinds of superfinishing stones. Specifically, it is judged that, up to the degree where the pressurizing force is greater by 15% (xcex8=30xc2x0) than the pressurizing force when the superfinishing stone is not inclined (xcex8=0xc2x0), there can be generally maintained a good condition without the superfinishing stone being chipped; and, in the case of 10% increase (xcex8=25xc2x0) of the order, the superfinishing stone can be used stably, that is, this range can be considered as a practical use range. Further, in the case of xcex8=20xc2x0, the pressurizing force may only be increased by about 6.5%, that is, in this condition, the superfinishing stone can be used more stably.
Also, according to a second aspect of the invention, there is provided a superfinishing apparatus of a tapered roller bearing in which, while rotating an outer ring of a tapered roller bearing about a center axis, the leading end face of a straight-shaped superfinishing stone inserted from a front face of outer ring is slidingly contacted with a taper-shaped raceway surface formed in the inner peripheral surface of the outer ring to thereby superfinish the raceway surface, wherein a superfinishing stone holder holds the superfinishing stone by inclining the superfinishing stone outwardly of the front face of outer ring with respect to the vertical line of the raceway surface.
According to the superfinishing apparatus of the second aspect, in case where the superfinishing stone is held by the superfinishing stone holder, the thus-held superfinishing stone is held in such a manner that it is inclined outwardly of the front face of outer ring with respect to the vertical line of the raceway surface. Therefore, simply by setting the superfinishing stone on the superfinishing stone holder, interference between the rear end portion of the superfinishing stone and the non-working raceway surface can be avoided. This makes it possible to use a long-sized superfinishing stone, which can reduce the frequency of replacement of superfinishing stones and thus can enhance the working efficiency of the superfinishing apparatus.
Further, according to a third aspect of the invention, there is provides a superfinishing apparatus of a tapered roller bearing in which, while rotating an outer ring of a tapered roller bearing about a center axis, the leading end face of a straight-shaped superfinishing stone inserted from a front face of outer ring is slidingly contacted with a taper-shaped raceway surface formed in the inner peripheral surface of the outer ring to thereby superfinish the raceway surface. Wherein an automatic superfinishing stone feed-out mechanism for holding the superfinishing stone by inclining the superfinishing stone outwardly of the front face of outer ring with respect to the vertical line of the raceway surface and also for moving the superfinishing stone to the leading end side thereof depending on the consumption of the leading end face of the superfinishing stone.
According to the superfinishing apparatus of the third aspect, when the leading end face of the superfinishing stone is worn, the superfinishing stone is moved to the leading end side thereof, so that the effective use length of the superfinishing stone can be automatically consumed down to the extreme end portion thereof. Therefore, when compared with a conventional operation in which short superfinishing stones are replaced frequently, the apparatus stop time for superfinishing stone replacement as well as the time and labor necessary for superfinishing stone replacement can be reduced greatly.
Also, in the superfinishing apparatus of the third aspect, the automatic superfinishing stone feed-out mechanism may includes a holder part disposed on an oscillation table for receiving and holding the superfinishing stone in the above-mentioned inclined state, a pressurizing/feed-out cylinder disposed on the holder part for pressurizing the superfinishing stone received in the holder part in the leading end direction of the superfinishing stone, a superfinishing stone wearing detect dog disposed on the holder part and movable simultaneously with the feed-out of the superfinishing stone, and a detecting device fixedly secured to the holder part and is actuated by the superfinishing stone wearing detect dog for detecting the wearing amount of the superfinishing stone.
According to the thus structured superfinishing apparatus, the superfinishing stone received in the holder part can be arranged at a given position of the raceway surface due to the movements of an XY table and the oscillation table. And, the superfinishing stone received in the holder part can be fed out in the leading end direction thereof in a posture in which its interference with the non-working raceway surface is prevented. Such feed-out of the superfinishing stone is attained, for example, by pushing the rear end face of the superfinishing stone by the pressurizing/feed-out cylinder disposed on the rear end portion of the holder part. And, when the superfinishing stone is fed out sequentially due to wearing thereof and the superfinishing stone wearing detect dog being moved together with the superfinishing stone reaches the fixed position of the detecting device, the detecting device is actuated to detect a given wearing amount of the superfinishing stone, to thereby notice the time of replacement of the superfinishing stones.
In this specification, a xe2x80x9cnon-working raceway surfacexe2x80x9d represents a raceway surface position of an outer ring such that is situated at a region that the raceway surface position of the outer ring is not subjected to working when the outer ring is worked by the superfinishing stone. Thus, a raceway surface position 35b of FIG. 1 situated opposite to a raceway surface position 35a contacting with the superfinishing stone is defined as the xe2x80x9cnon-working raceway surfacexe2x80x9d.